Question

why do vc cycle systems typically use 10 to 20 degrees fahrenheit of sub schooling?

Why do vc cycle systems typically 10 to 20 degrees fahrenheit of super heating?

Answer 1

The vapor compression (VC) cycle system consists of seven stages. Two of which are sub-cooling and superheating.

• Additional temperature decrease during conversion of vapor to liquid which involves removal of heat from the refrigerant at its saturation condensing temperature is called sub-cooling. It happens in the system’s condenser.
• Additional temperature increase above the boiling point during conversion of the refrigerant from liquid to vapor which involves addition of heat to the liquid at its saturation temperature is called superheating. It happens in the system’s evaporator.

Answer (1):

VC cycle systems typically use 10 to 20 degrees Fahrenheit of sub-cooling

• Refrigerant normal cooling temperature is between 10 to 20 degrees.
• When the temperature falls below 10 degrees:
  • Refrigerant didn’t lose ‘normal heat amount’ during its flow through condenser.
• When the temperature rises above 20 degrees:
  • Refrigerant got cooled more than that of normal.
• A few consequences of improper cooling temperature are as follows:
  • Overcharge
  • Undercharge
  • Insufficient condenser airflow

Answer (2):

VC cycle systems typically use 10 to 20 degrees Fahrenheit of super heating

• The normal 10 to 20 degrees temperature make sure that the compressor draws only vapor (no liquid refrigerant).
• When the temperature falls below 10 degrees:
  • It implies that refrigerant didn’t have enough heat in the evaporator to fully boil into vapor.
  • Liquid refrigerant will be drawn which causes:
    • Slugging (damage of the compressor valves)
    • Premature failure (if mixed with oil)
• When the temperature rises above 20 degrees:
  • It implies that refrigerant got more heat than normal, which may lead to:
    • System undercharge
    • Refrigerant restriction
    • Excessive evaporator heat loads